Submarine and long-distance telephone system and method of operating the same



May 27,1924. 1,495,926

L. RELLSTAB' SUBMARINE AND LONG DISTANCE TELEPHONE SYSTEM AND METHOD OF OPERATING THE SAME Filed July 8, 1922 i g i -i i i i I H E E A m i =2 i citizen of Germany, and residing 45 the line and balancing circuit.

Patented May 27, 1924.

UNITED STATES LUDWIG RELLSTAB, on ZEIST; NEAR Urnncnm,

PAT

NETHERLANDS, ASSIGNOR TO NAAM- LOOZE VENNOOTSOHAP DE NEDERLANDSCHE THERMO-TELEPHOON MAATSCHAP- PIJ, O'F UTRECHT, NETHERLANDS, A CORPORATION OF SUBMARIN E AND LONG-DISTANCE TELEPHONE SYSTEM ANT) METHOD THE SAME.

Application filed July 8,

To c ll whom it may concern:

Be it known that I, LUDWIG RELLSTAB, a at Zeist,

near Utrecht, in the Netherlands, have invented certain new and useful Improvements in Submarine and Long-Distance Telephone Systems and Methods of Operating the Same (for which I have filed an application in-Germany March 5, 1921), of 1 which the following is a specification.

My invention relates to improvements in submarine and long-distance telephone systems and the method of operating the same. In submarine telephone systems intensifiers or amplifiers can be provided only at the terminals of the cable, and they can not be mounted within the cable itself, because they require a continuous supply of energy and supervision. By providing Pupin c0118 the cost of the cable is increased and in addition the cables are more rapidly worn out, the said coils being disposed internally of the covering ofthe cable. For these reasons Pupin coils have been provided in submarine cables only in exceptional cases.

If amplifiers are provided only at the terminals of the cable, the sound transmitting current must be much stronger at the inputend of the cable than at the output end thereof, and for speaking over long distances a considerable quantity of energy must be supplied to the transmitter. When generating and modulating a part or all of the said energy at the station of the subscriber, ob-

jectionable effects on the subscribers receiver can not easily be avoided. Heretofore the means provided to obviate this objection aimed at compensation of the efl'ects of the energy of the transmitter current on the 40 receiver of the speaking subscriber, for example by means of a subsidiary or balancing circuit connected to the subscribers line and by differential connection of the coupling members of the transmitter or receiver and However, such means fail in case of high energy, because the subsidiary conductor or balancing circuit can never be made equal to the actual line, the actual line being subject to variation in capacity, resistance and leaking by changes of temperature.

The object of the improvements is to ob- NETHERLANDS.

OF OPERATING viate as far as 1n long-distance telephones, and with this ob ect in view my invention consists in transmitting-the telephone sounds by means of two different forms of energy, the microphone batterymf the speaking subscriber generating the ordinary currents, which are transmitted to and through the cable to the distant terminal oflice thereof or the telephone central oflice to which the receiving subscribers station is connected, and which are transformed in the said oflice according to the principles of high-frequency telephony, so that the sounds are transmitted from the said oflice over the subscribers line to the receiving apparatus by high frequency means. When speaking in the opposite dire'ction conditions are reversed.

In addition in my improved system disturbing noises caused by foreign influences are reduced, which noises have ordinarily low-frequency character and are not reproduced by the high-frequency apparatus.

. For the purpose of explaining the invention an example-embodying the same has been illustrated in the accompanying drawing, in which a diagram of the apparatus and circuit connections is shown.

In the said drawing two subscribers stations, A and B, are shown, connected by line circuits f and m respectively, to terminal offices or telephone exchanges CO and CO between which extends a submarine cable or long distance telephone line 12. The'microphone 0 of the subscriber A is supplied with energy from a battery (1 located at the possible the said objections telephone ofliceCO through a choking coil 0 and the subscribers line 7. When speaking the subscriber causes alternating current to a is very powerful.

At the telephoneofiice CO the subscribers line 7 is compensated by a subsidiary circuit m, and a setof coils n, 0, 0' is connected between the subscribers line f and the subsidiary line 122.. The function of the said coils is known to those skilled in the art, the coils o-0" being opposite in effect with respect to their common secondary 0 as regards currents generated in coil 91., but cumulative as regards currents through the line) originating at station A. I v

The differentially connected transformers 0, 0' act through secondary 0 on a lowfrequency intensifier or amplifier y of high amplifying power and high energy discharge, the energy of which is used for overcoming the impedance of the cable line.

The long distance cable ;0 is compensated at both terminals by subsidiary balancing circuits q and 1- as is known in the art. Between 9 and p at the transmitting terminal and between p and r at the receiving terminal differentially connected groups of coils s, t, t and u, v, a respectively are provided; The alternating currents from the speaking subscribers microphone at station A, amplified as described at y flow through the cable ;0 in the form of low frequency currents, and they pass through the transformers 4), 0, the secondary voltages of which are added to each other, and so are repeated into the high-frequency generator and amplifier w, which intensifies the oscillations and produces a high-frequency alternating carrier current the frequency of which is far above the frequency of acoustic oscillations. The said high-frequency current is modulated to oscillate with reference to its amplitude at the rate of the currents from the'speaking subscribers station, and in this form it is transmitted to and throu%h the line as of the receiving subscriber, which is connected in the same way as the line 7 of the transmitting subscriber. The high-frequency current acts, by means of the transformers z and h, on the thermic tele' phone is andca-uses therein the reproduction of the sounds, the thermic telephone having the property of transforminga modulated high-frequency current into low-frequency acoustic oscillations.

I have thus made clear the propagation of sound waves or oscillations originating as low frequency current waves at station A, through the intervening line f and cable p, and their transmission through line w to station B as modulations on'a high frequency carrier current supplied at the terminal amplifier and generator w. It is apparent from the arrangement shown in the drawing that voice waves originating at the transmitter c at station B will be propagated in the same manner through line :0, the low frequency amplifier 3 at terminal CO and the cable p to the terminal ofiice' CO, where through coils t, t, (cumulative in effect for cable currents) they will be repeated into the high frequency generatormodulator-amplifier unit and will thence be transmitted as modulations on a high frequency carrier current through the subscribersline f to the station A, where they will affect the thermic receiving telephone. Thus, a two way system is provided, in which currents are transmitted in each direction through successive links or sections (land line-cableland line) at different frequencies, opposite currents in either land line, i. e. currents for sending and for receiving respectively, being of difierent and separable frequencies, and .all currents through the cable '(or equivalent long distance line) being of low or voice frequency, but great power.

By reason of my improved system I am enabled to use at the subscribers stations microphones of any power without providing amplifiers, batteries, and the like, theother hand the high-frequency currents can be strong, without reacting on the long-distance line, because any high-frequency current which mi ht pass through the coils 0, 0', 0 into the ow frequency amplifier y, or

1 as the case may be, having imperfect differential action, are intensified to a minimum degree and thereafter are entirely annihilated within the long-distance line p by damping.

Preferably a condenser 2 of a capacity of microfarad is connected in shunt across the low-frequency intensifier 3 which does not materially reduce the low-frequency ourrents, it representing as against such cur- I rents a high resistance of. about 1000 ohms, while as against-high-frequency currents it acts as a short-circuit of 10 ohms.

WVith this system I am enable-d more thoroughly to keep apart the transmitted lowfrequency current and the received highfrequency current, than is possible with ordinary telephone systems. The long-distance line 72 as well as the subscribers lines 7 and m 'being balanced by subsidiary circuits g, 1' and m, g, m, respectively, the. separation of t e outgoing'and received currents is particularly complete.

Vhen it is desired to use my invention vided that the said means are disposed between the ends of the long-distance line itself.

The advantages of my improved system are available also for long-distance land lines, though they are less conspicuous in such use than in use with submarine cables.

I claim:

1. In a telephone system two local or subscribers stations each containing a microphone transmitter and a high frequency wave receiver, and a wire circuit connecting them for conversation composed of three links or sections, the two end links communicating directly with the respective local stations, and an intermediate trunk line having inductive terminal connections with the end links, said inductive connections including a low frequency amplifier for the input from each end link into the trunk line, and a high frequency generator and modulator unit for the output from each end of said trunk line into the corresponding end link, whereby voice waves originating in the trans mitter at each local station will pass thence through the corresponding end link and its low frequency output amplifier into and through the trunk line at the same low frequency, and at the distant end thereof will be transformed into corresponding low frequency modulations on a high frequency carrier current and so propagated in the distant end link to be detected and rendered audible by the subscribers or local station wave receiver connected thereto, the currents transmitted and received respectively through each end link or subscribers line being of different character and frequency, and non-interfering, and all power for amplifying and transforming being supplied at the two ends of the intermediate link.

2. The system claimed in claim 1 in which the inductive terminal connections are re-,

peating coils differentially connected as between each land line or end link and the respective low frequency amplifiers and high frequency generators and intensifier-s, and as between the same and the ends of the trunk line, whereby low frequency and high frequency currents are kept separate, and low frequency current will not be repeated back into the originating line, nor high frequency currents back into the trunk.

3. The system claimed in claim 1 in which the inductive terminal connections are repeating coils differentially connected as between each end link and the respective low frequency amplifiers and high frequency generators and intensifiers, and as between the same and the ends of the trunk line, with a low capacity condenser connected in shunt of the repeating coil winding on the input side of the low frequency amplifier to short circuit high frequency currents that pass through said repeating coil.

4. The system claimed in claim 1 with inductive terminal connections consisting of repeating coils differentially connected as between each land line or end link and the respective low frequency amplifiers and high frequency generators and intensifiers, and as between the same and the ends of the trunk line, and artificial balancing lines at both ends of the trunk line, each artificial line or balancing circuit containing a corresponding balancing winding of the terminal repeating coils.

5. A telephone system comprising a cable with terminal ofiices containing the terminals of subscribers lines, a low frequency ampli-' fier connected for input, and a high frequency generator, modulator and amplifier unit connected for output, at each end of the cable, a subscribers line terminating at each of said central stations, a subscribers station on each line, having a microphone transmitter and a high frequency receiver, a

source of current at each terminal oflice connected-to supply energy over the line for the subscribers transmitter, and differential repeating coil connections between each line and cable including the said amplifier and said high frequency unit, respectively.

In testimony whereof I hereunto affix my signature in presence of two witnesses.

LUDi/VIG RELLSTAB. Vitnesses H. Y. Korrnns, T. V. SHANGENDYK. 

